Wind turbines are used to convert mechanical wind energy to electrical energy in a clean and efficient way. In a wind turbine a mechanical drive train comprising a wind rotor with several rotor blades drives an electric generator, either directly or by means of a gearbox. The resulting alternating current (AC) frequency that is developed at stator terminals of the electric generator is directly proportional to the speed of rotation of the wind rotor.
In order to provide an AC power signal being matched with a utility grid a wind turbine comprises a power converter, which includes a generator side AC-DC converter, a DC bridge, and a grid side DC-AC converter. The AC-DC converter and the DC-AC converter typically comprise several high power semiconductor switches which are arranged in a bridge configuration for each phase of the AC current.
Wind turbines can be erected on-shore or off-shore. Large wind turbines are typically installed off-shore. In particular for maintenance reasons self-excited generators having a rotor assembly with permanent magnets are employed. For efficiency reasons an air gap between (a) the coils of stator segments of the stator assembly and (b) the (permanent) magnets of the rotor assembly should be kept small. Therefore, such a large generator must be built up with an extreme high constructional precision. Further, the large size of such a generator requires special solutions not only for assembling but also for maintaining the generator. A maintenance work may include e.g. an exchange of a magnet on the rotor side and an exchange of a stator segment on the stator side. It is obvious that for maintaining a generator a rotation of the rotor assembly with respect to the stator assembly must be prevented.
EP 2 566 017 A1 discloses a generator for a wind turbine. The generator comprises a stator assembly, a rotor assembly, and at least one rotor brake disk. The rotor brake disk extends in radial outward direction. Thus, an air gap extending between the stator assembly and the rotor assembly is freely accessible at all times from an axial direction leading to improvements regarding serviceability, particularly concerning an axial insertion or removal of magnets and stator segments.